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A series of Co-Sn alloys was solidified. It was found that the as-cast microstructure of the Co-20.5at.%Sn alloy, which on the basis of literature reports has long been thought to be the eutectic composition, contains much primary phase besides lamellar eutectics. The cooling curve of this alloy contains two exothermic peaks. In contrast, when a Co-24.0at.%Sn alloy was solidified, an entire lamellar eutectic was obtained in the as-cast microstructure. Also, the thermal analyses indicate that there is only one solidification reaction in this alloy. It is suggested that the actual eutectic composition of the Co-Sn system is around Co-24.0at.%Sn, and the corresponding eutectic temperature is about 1385 K.

A series of Ni-P alloys (Ni-rich) have been synthesized and solidified. It is found that the solidification microstructure of the Ni-19.0 at.%P alloy that has long been regarded as the eutectic composition contains many primary phase dendrites besides rod eutectics. In contrast, only rod eutectic microstructure appears in the samples of Ni-19.6 at.%P, and this alloy shows the lowest end temperature of melting among all the compositions investigated. The results indicate that the actual eutectic composition at the Ni-rich part of the Ni-P system is Ni-19.6 at.%P. The eutectic temperature is determined to be about 1163 K by the differential scanning calorimetry analysis.

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